Nowadays a large variety of applications are based on solid nanoparticles dispersed in
liquids—so called nanofluids. The interaction between the fluid and the nanoparticles
plays a decisive role in the physical properties of the nanofluid. A novel approach
based on the nonradiative energy transfer between two small luminescent nanocrystals
(GdVO4:Nd3+ and GdVO4:Yb3+) dispersed in water is used in this work to investigate
how temperature affects both the processes of interaction between nanoparticles and
the effect of the fluid on the nanoparticles. From a systematic analysis of the effect
of temperature on the GdVO4:Nd3+ → GdVO4:Yb3+ interparticle energy transfer, it
can be concluded that a dramatic increase in the energy transfer efficiency occurs for
temperatures above 45 °C. This change is properly explained by taking into account
a crossover existing in diverse water properties that occurs at about this temperature.
The obtained results allow elucidation on the molecular arrangement of water
molecules below and above this crossover temperature. In addition, it is observed
that an energy transfer process is produced as a result of interparticle collisions that
induce irreversible ion exchange between the interacting nanoparticles.